Advances in engineering and technology often place severe new demands on the support systems for machine components that require relative movement both in terms of improved performance and increasingly demanding operating conditions. The vast majority of these demands are resolved through a combination of intelligent design of "conventional" bearing systems, the development of improved liquid lubricants for a wide range of specialized applications and the creation of effective sealing techniques for the circumstances in which it is Essential Minimize leakage of lubricating liquids or their vapours.
However, in an increasing number of applications it is necessary to achieve a result that is technically or economically impracticable with conventional lubricants. Numerous alternative classes of bearing systems have been designed to meet new needs by means of adapting to similar circumstances. For example, in a vacuum, a magnetic medium (for low temperatures) may be used; To handle virtually any liquid, the liquid itself can be used as a lubricant although it may lack numerous convenient qualities available with lubricating oils; And for numerous special purposes, including some applications at very high temperatures, solid lubricants such as graphite or molybdenum or tungsten disulfide may be employed. Another alternative class of bearings is the use of a gas (air) as a lubricant. Air lubrication offers certain unique advantages because in its own way and place do the other alternatives but also air bearings have their own inherent limitations which must be clearly recognized in advance if the aspiring user is to avoid unjustified failure.
In particular, it should be recognized that air bearings of virtually all types are somewhat more prone to instability difficulties than liquid bearings, although most of these instabilities are largely of the same general type as occur in lubricated systems With liquid; For example, the important case of half-speed spin in the daily 360-degree action itself. The bearings under pressure also have their instability problems although they are sometimes of a very different type. Air bearings (also known as aerostatic or aerodynamic bearings) are bearings that use a thin film of pressurized air to provide an interface of excessively low friction loading between surfaces. The two surfaces do not touch. As they are free from contact, air bearings avoid traditional friction bearing, wear, particle and lubricant handling problems, and offer distinct advantages in precision positioning, such as lack of play and static friction, as well as High speed Applications.
The fluid film of the bearing is air flowing through the bearing itself to the bearing surface. The design of the air bearing is such that, although air escapes constantly from the bearing gap, the pressure between the bearing faces is sufficient to withstand the work loads. Thus, there is a differentiation that has to be made between the aerodynamic bearings, which establish the air cushion through its movement, and the Aerostatical bearings, in which the pressure is being inserted externally.
